Carly Simon Back In Form With New Lp

''I feel I've established myself in music and there's a lot more I can do,'' she said. ''I'd like to write a musical comedy, I'd like to score a symphony.''

After a two-year absence, the elusive pop diva has just released the LP Spoiled Girl (Epic), which has made her a hot number with the press again.

At 40, Simon has come into her own. She is no longer the flake who might suffer from crippling stage fright. No longer the neurotic wife writing songs in the shadow of a famous and troubled recording artist. No longer the dismissible little rich girl of the Simon in Simon & Schuster.

Her video of ''Tired of Being Blonde'' is a giggle, and she's getting raves for her pre-release video of ''My New Boyfriend.'' In the last, she plays Cleopatra, Sheena and a modern woman in a beauty parlor. The song -- the most upbeat on the album -- is being remixed for clubs.

She is also at work writing an entire musical score (her first) for the movie Heartburn, based on Nora Ephron's book and starring Meryl Streep. The song for the final scene of the movie -- which she recorded with her kids -- is nearly completed, and she said the response has been more than she had hoped for.

''Meryl and Nora called me and said the song made them cry,'' she said in her Central Park West kitchen, where scads of Polaroids, mostly of her two kids -- Ben, 8, and Sally, 11 -- line the wall.

Simon's songs always have been largely autobiographical -- which has made her personal life fair game. Just who was the man with the apricot scarf who was so vain he probably thought that song was about him?

''What I sing about is me,'' she said, ''but I don't ever reveal all of myself -- it branches into fiction. People assume my writing is a lot more literal than it is. But very often, it's what friends were going through -- or I just needed another verse.''

Does that mean she's not tired of being blond?

''Hey!'' she quipped. ''I just finished streaking my hair!''

Well, what about this ''spoiled girl'' business?

''It's the devil in all of us,'' she said, strutting across her living room floor. ''It's not being satisfied with what you have:

'When you got a pretty boy

You wanna smart one

When you got a smart one

You want him pretty

When you got one who's all over you

You wish he'd hold back

Then when he's being cool

you want him to attack.'

''The spoiled woman has a sense of herself, enough that she feels she deserves whatever she wants.''

Simon's changes of heart are well known. Her divorce from James Taylor and her romance with actor Al Corley were well-publicized, as has been her upcoming marriage to Taylor's old friend and drummer, Russ Kunkel -- the one she wrote ''Tonight and Forever'' for. Now she says there has been a schedule conflict and the wedding has been postponed.

''At some point there will be a wedding,'' said Simon. ''Marriage is mainly important when there are children involved. The reason now is I'm in love with someone I want to marry. He has children and I have children and we want to combine them and make a family.

''When I married James,'' she said, ''I wanted to make a statement to myself and to the world. And, we wanted to have children. You can't straighten anyone else out. They have to straighten out themselves. He's straight now. Our relationship with him now is of two divorced parents. We share two incredibly wonderful children we're very proud of. I think we're proud of each other.''

What is she looking for in a husband now?

''The most important thing is that he have a great body,'' she deadpanned. ''No, don't write that. The most important thing is that there be honesty, that there be a lot of room to grow in -- in more colloquial terms, space. I believe in monogamy. I've certainly experimented with alternatives.''

At her last concert, in 1980, Simon suffered an acute ''anxiety attack'' that caused her to walk off the stage. Now she thinks she might like to finish that tour. ''I'd like to tour the world, by motorcycle, nude . . . I like to keep all doors open.''